Taliban gunmen armed with rockets and explosives stormed a major naval air
base in the heart of Karachi, Pakistan's biggest city, destroying two
US-made surveillance aircraft and killing 12 personnel.

It was the worst assault on a military base since the army headquarters was besieged in October 2009, piling further embarrassment on the armed forces three weeks after US troops killed Osama bin Laden under their noses.

Up to 20 militants crept into the base in the teeming port city of Karachi from three sides under the cover of night late Sunday, officials said, triggering gunbattles and a series of explosions.

More than 12 hours later, officials were unable to confirm that the attack on the PNS Mehran, a sprawling compound of the Pakistani navy's air arm, was over. By mid-morning, fire crews had doused towering flames over the base.

Rehman Malik, the interior minister, said the "terrorists" sneaked into the base from three points adjacent to residential areas in the city of 16 million people, whose port is a vital hub for Nato supplies bound for Afghanistan.

"A (single-storey) building in the premises is still under their occupation from where they are exchanging fire with our soldiers," Mr Malik said.

"It is not just an attack on a navy establishment, it is an attack on Pakistan," Mr Malik added, warning that those who sympathise with the Taliban and al-Qaeda should instead "join hands with us to save our country".

A spokesman for the Pakistani Taliban, who have stepped up attacks claiming to avenge the May 2 death of bin Laden, said the militia had dispatched 15 to 20 suicide bombers equipped to fight for a week.

"We had already warned after Osama's martyrdom that we will carry out even bigger attacks," a Taliban spokesman Ehsanullah Ehsan said.

"Our people present inside are all fedayeen (suicide bombers). They are 15 to 20 in number and were sent after proper planning. They can fight for one week and until they embrace martyrdom," he said.

The al-Qaeda leader was killed by US commandos in a garrison town north of Islamabad, in a raid that humiliated Pakistan's security establishment. The militants' attack deep inside Karachi underlined the military's vulnerability.

Navy spokesman Commander Salman Ali said that 11 navy officials and one paramilitary force member had been killed in exchanges of fire with the militants, who he said numbered from 10 to 15.

"They have destroyed two P-3C Orion aircraft," he added. The United States delivered the two maritime patrol aircraft to PNS Mehran only last June.

The attack was also likely to raise further concerns about the safety of Pakistan's nuclear weapons, which reportedly number more than 100.

The New York Times said that a mere 15 miles away from PNS Mehran, Pakistan was believed to keep a large depot for nuclear weapons that can be delivered from the air.

Karachi is Pakistan's financial capital and its port is used by NATO to ship supplies to the estimated 130,000 US-led foreign troops fighting the Taliban in neighbouring Afghanistan.

The assault was the fourth on the navy in Karachi in a month. Three bombings in late April killed nine people, including eight naval personnel.